A radiation window is a part of a measurement apparatus that allows a desired part of electromagnetic radiation to pass through. In many cases the radiation window must nevertheless be gastight, in order to seal and protect an enclosure where reduced pressure and/or a particular gas contents prevail. The pressure inside the enclosure may be also higher than outside, for example in measurement apparata on board space-going platforms. In order to cause as little absorption as possible of the desired radiation, a major part of the radiation window should consist of a very thin foil.
Patent applications number PCT/FI2010/050781 (published as WO2011/151505) and PCT/FI2011/050100 (published as WO2011/151506) disclose a manufacturing principle, according to which a silicon wafer or a corresponding piece of etchable material is used as a temporary carrier during the manufacturing process of a radiation window. A so-called etch stop layer is produced on a polished surface of the temporary carrier. The etch stop layer is meant to eventually remain as a part of the completed radiation window. Further layers of the radiation window are produced on the etch stop layer using thin film manufacturing techniques, such as CVD (chemical vapour deposition), ALD (atomic layer deposition), and/or PLD (pulsed laser deposition). After the completion of adding layers, window blanks are cut out, with the temporary carrier still present giving additional support and enabling easier handling. A window blank is attached to a frame, after which the exposed temporary carrier is not needed any more and can be etched away. The etching is conveniently stopped by the etch stop layer, leaving only the layered radiation window foil attached in the frame. The result is a completed radiation window, the frame of which can be used for attaching it into place in a measurement apparatus.
Despite its many advantages, the manufacturing method described above still leaves room for finding other advantageous methods for manufacturing radiation window foils and radiation windows.